Devices and Methods for Wireless Power Harvesting and Backscattering Communications

The present disclosure relates generally to devices and methods for providing wireless power harvesting (WPH) and backscattering communications, and in particular to devices and methods for providing WPH and harmonic backscattering (HB) communications.

Simultaneous Wireless Information and Power Transfer (SWIPT) transceivers are poised to play a significant role in the Internet of Things (IOT) and Wireless Sensor Network (WSN) applications. To be compatible with SWIPT transceivers and be able to interrogate them, scattered IoT and WSN devices are designed as a receiver and a transmitter at the same time. Backscattering technology draws vast attention and interest as it reflects incoming radio frequency (RF) signals from SWIPT transmitters for communications instead of re-generating them, significantly saving energy. A self-sustainable backscattering device may be possible by drawing power from incident RF signals from SWIPT transceivers and reflecting backscattered signals.

According to one aspect of this disclosure, there is provided a self-adaptive backscattering device, comprising an antenna for receiving and transmitting radio frequency (RF) signals; a non-linear element coupled to the antenna; and a switch for operably coupling the non-linear element to a wireless power harvesting (WPH) load, wherein when the switch is on, the non-linear element is connected to the WPH load for harvesting RF signals incident on the antenna to direct current (DC) energy in a WPH mode; when the switch is off, the device switches from the WPH mode to a harmonic backscattering (HB) mode for transmitting harmonic backscattered RF signals through the antenna, and the switch self-adaptively switches between on and off based on harvested DC energy.

In some implementations, the switch is switched off when the harvested DC energy in the WPH mode increases to a first level; and the switch is switched on when the harvested DC energy decreases to a second level, wherein the first level corresponds to a logic high bias of the switch; and the second level corresponds to a logic low bias of the switch.

In some implementations, the device further comprises an energy storage for storing the harvested DC energy; and at least one sensor powered by the energy storage for generating sensor information.

In some implementations, at least one sensor starts functioning when the harvested DC energy in the WPH mode reaches a sensor threshold; the sensor is adapted to convert the sensor information into high and low bias voltages to switch off and on the switch; and the antenna is adapted to transmit the harmonic backscattered RF signals carrying the sensor information.

In some implementations, the sensor information is converted into high and low bias voltage using ON-OFF Keying (OOK) modulation.

In some implementations, the device further comprises an input matching network and an output matching network, wherein the input matching network is adapted to maximize input power transfer of the incident RF signals at f, the output matching network is adapted to maximize output power transfer to the harmonic backscattered RF signals of 2fin the HB mode.

In some implementations, the device further comprises two quarter-wavelength stubs each connected to an end of the non-linear element for filtering and maximizing harmonic backscattering of the incident RF signals, wherein the two quarter-wavelength stubs can help the non-linear element maximize its conversion from incident RF signals of fto the harmonic backscattered RF signal of 2f.

In some implementations, the device further comprises a filtering capacitance connected to the WPH load for grounding fundamental and higher harmonic RF signals in the WPH mode.

In some implementations, the non-linear element comprises a single Schottky diode.

In some implementations, the switch is a Single Pole, Single Throw (SPST) switch and the device initially operates in the WPH mode.

According to another aspect of this disclosure, there is a self-adaptive method of wireless power harvesting (WPH) and harmonic backscattering (HB), comprising receiving radio-frequency (RF) signals from a transceiver; converting the RF signals into direct current (DC) power in a WPH mode via a non-linear element; and automatically switching from the WPH mode to a HB mode for generating harmonic backscattered RF signals via the non-linear element, based on the converted DC energy.

In some implementations, the transceiver is a simultaneous Wireless Information and Power Transfer (SWIPT) transmitter.

In some implementations, wherein said automatically switching from the WPH mode to the HB mode comprises automatically switching from the WPH mode to the HB mode when the converted DC energy increases to a first level; and the method further comprises automatically switching from the HB mode to the WPH mode when the converted DC energy decreases to a second level, wherein the first level corresponds to a logic high bias of the switch; and the second level corresponds to a logic low bias of the switch.

In some implementations, the method further comprises turning on a sensor when the converted DC energy reaches a first threshold for generating sensor information.

In some implementations, the method further comprises converting the sensor information into high and low bias voltages for switching off and on the switch; and transmitting the harmonic backscattered RF signals carrying the sensor information.

In some implementations, the sensor information is converted using ON-OFF Keying (OOK) modulation.

In some implementations, said generating harmonic backscattered RF signals comprises upconverting and maximizing incident RF signals of finto second harmonic backscattered components of 2fusing the non-linear element and two quarter-wavelength stubs.

In some implementations, the method further comprises accumulating the harvested DC energy in an energy storage.

In some implementations, the RF signals are received in response to a request from a portable device; and the harmonic backscattered RF signals are transmitted to the portable device.

In some implementations, the switch is on by default to connect to a WPH load for initially operating in the WPH mode.

The various implementations disclosed herein provide a solution suitable for self-adaptive devices, methods, circuits and systems for WPH and backscattering communications, particularly WPH and HB communications.

By realizing WPH and backscattering functions using a shared nonlinear element, the system design can be simplified, efficiency increased, and the device's energy consumption reduced. Various of the embodiments of the described devices and methods adopt harmonic backscattering technology, which can reduce interference introduced by self-jamming. The various implementations disclosed herein provide self-adaptive and battery-free operations enabled only or otherwise substantially by incoming RF signals. Sensor information can be transmitted through the backscattering signals. The compact designs of the devices, methods, circuits and systems make them a cost-effective and energy efficient solution in many applications of WPH and HB communications, including but not limited to IoT and WSN applications.

Embodiments disclosed herein relate to devices, methods, circuits and systems of providing wireless power harvesting (WPH) and backscattering communications, particularly harmonic backscattering (HB) communications. The described embodiments of devices, methods, circuits and systems can be suitable for use in wireless communications using radio frequency (RF) signals, including but not limited to Internet of Things (IoT) and Wireless Sensor Network (WSN) applications. Examples of the RF signals include but are not limited to digital television broadcasting, Global System for Mobile communication (GSM™), Long Term Evolution (LTE™), Wi-Fi™ signals, Bluetooth™, and the like.

For purposes of this disclosure, WPH refers to devices, methods, circuits and/or systems that can receive RF signals and convert them into direct current (DC) energy or power. The converted DC energy or power can be used to drive various parts of the system or circuit, including for example, one or more sensors.

Backscattering refers to devices, methods, circuits and/or systems that can reflect incident signals, such as RF signals, back to the space for communication purposes. Such devices, methods, circuits and systems do not re-generate signals to reduce power consumption.

Harmonic backscattering refers to devices, methods, circuits and/or systems that can upconvert the operating frequency when reflecting incident signals. Those skilled in the art can appreciate that while harmonic backscattering may be described in the context of doubling the operating frequency according to various embodiments of this description, the harmonic backscattering module or method can triple, or quadruple the operating frequency or more, depending on the specific designs and applications of the systems.

Battery-free and self-sustainable IoT or WSN devices are designed to communicate with and powered by a Simultaneous Wireless Information and Power Transfer (SWIPT) or similar transceiver which uses RF signals for both wireless information transfer (WIT) and wireless power transfer (WPT) at the same time.

Various designs for ambient backscatter transceivers have been proposed. For example,illustrates an IoT or WSN deviceinteracting with a SWIPT or similar transceiver. The devicecan comprise an antenna, a WPH moduleand a backscattering module, where both the WPH moduleand the backscattering moduleare standalone modules. The deviceoften requires a microcontroller (MCU)which can be energized by the WPH moduleto control the backscattering communication with the SWIPT or similar transceiver, or other distributed devices (not shown). Such IoT or WSN devicemay receive RF power and convert them into DC to drive the entire deviceor may rely on additional energy sources, such as solar, mechanical, or thermal sources to power the various components.

Conventional devices and methods primarily realize WPH or backscattering as standalone functions. When integrated into a single platform, WPH and backscattering functions are often implemented by separate modules, which can result in a complicated design, a large volume factor, as well as high power consumption. Controlling the operations of WPH and backscattering typically relies on a separate MCU, which consumes additional power.

These designs often employ a WPH moduleto collect RF energy or other types of energy (such as solar, thermal, mechanical energy or the like) in order to power backscattering communications, MCUs, and/or sensors (not shown). As a self-sustainable platform, more separate modules involving active components can translate into more losses, resulting in a more power-hungry platform.

Backscattering communications are realized by reflecting incident RF signals to the transceiver. As backscattering signals have the same frequency as the incident ones, which can cause self-jamming problems. Thus, to avoid such problems, various devices and methods may introduce extra modules and energy to shift backscattering RF signals to other frequency bands. One example of a frequency-shifted backscattering device uses a ring oscillator to move the frequency of reflected signals to another frequency band, different from that of the incoming ones. Another example of a frequency-shifted backscattering device uses a mixer to shift backscattering signals.

Some backscattering devices therefore may incorporate complex MCU system architecture for operations. Complex system structure can add extra burden to the designs, overall power consumption, and/or cost.

Turning now to, a self-adaptive backscattering deviceaccording to some examples of this disclosure is shown. The self-adaptive backscattering devicecan be wirelessly powered by the SWIPT or similar transceiversand communicate with the SWIPT or similar transceiversusing backscattering technology, such as harmonic backscattering (HB) technology. The backscattering deviceis suitable for use as an IoT, WSN, or similar distributed device. As will be explained below, the backscattering deviceis self-adaptive and can be battery-free.

In the embodiment as shown in, the devicecomprises an antenna, a non-linear element, and a switch. The antennacan comprise any suitable structure for receiving and transmitting RF signals. The antennais adapted to communicate with the SWIPT or similar transceivers, or other distributed devices. The non-linear elementcan be operably coupled to the antenna. In one implementation, the non-linear elementmay comprise a single diode. The switchoperably couples the non-linear elementto a WPH load or energy storage. The WPH load or energy storageis adapted to accumulate DC energy or power harvested from incident RF signals. One non-limiting example of the energy storagecomprises a super capacitor.

As will be explained in more details below, the devicecan self-adaptively turn on and off the switchbased on the harvested DC energy, alternating between a WPH mode and a backscattering mode. In particular, when the switchis on (by default), the non-linear elementis connected to the energy storageand the deviceoperates in a WPH mode for harvesting or otherwise converting RF signals incident on the antennato DC energy. This path of connecting the non-linear elementto the energy storageor WPH load is generally denoted as path(as shown in), and can be referred to as the WPH path. When the switchis off, the deviceswitches from the WPH mode to the backscattering mode for transmitting backscattered RF signals (such as harmonic backscattered RF signals) through the antenna. The path of returning incident RF signals through the non-linear elementis generally denoted as path(as shown in), and can be referred to as the backscattering path, or in some examples, the HB path.

The devicemay further comprise one or more sensors. The energy storagecan use the accumulated energy or power to turn on and off the sensor, which in turn controls the switchto transmit sensor information through the backscattering RF signals. In other words, the devicecan return sensor information for use of the SWIPT or similar transceivers, or other distributed devices, using backscattering technology.

For example, the sensorcan start functioning when the harvested DC energy in the WPH mode reaches a sensor threshold. The sensorcan be adapted to convert the sensor information into high and low bias voltages to switch off and on the switch. In one non-limiting implementation, the sensor information can be converted into high and low bias voltage using ON-OFF Keying (OOK) modulation. The sensor information can therefore be carried in the backscattered RF signals and transmitted through the antenna.

In an alternative embodiment, the one or more sensorsmay be loaded on the antennaand may not be energy driven. The sensor information can be converted into a frequency shift of the backscattering signals (e.g., harmonic backscattering) in the backscattering mode. For example, when a temperature sensor (not shown) is loaded on the antenna, temperature variations can change the resonant frequency of the antennaand further result in a backscattering component (e.g., second harmonic component) with a frequency shift. Based on the frequency shift, the receiving end can detect the temperature information. The sensor information can therefore be carried in the frequency shift of the backscattered RF signals and transmitted through the antenna.

illustrates functional elements of the self-adaptive backscattering device, according to some examples of this disclosure. In operation, a SWIPT or similar transceivercan send RF signals to the device. As described above, the RF signals transmitted by the transceivercan be (1) delivering power to the devicethrough path(i.e., WPH mode) and (2) backscattered by the devicelater for sending sensor information wirelessly through path(i.e., backscattering communications mode). In some implementations, the backscattered RF signals can be upconverted to harmonic components. In these embodiments, the backscattering communications mode is also referred to as HB communications mode.

As shown in, the deviceoperates in either WPH or backscattering communication modes, determined by the status of the switch. According to various embodiments of the disclosure, the switchcan be controlled directly or indirectly by the accumulated DC energy or power, making the device a battery-free standalone system.

During operation and with reference to, the switchis normally turned on and the device initially operates in the WPH mode. When accumulated DC voltage increases and reaches a first level (e.g., logic high bias), the switchis turned off which effectively switches the devicefrom the WPH mode to the backscattering communications mode and the accumulated DC energy and voltage in turn starts to decrease. When the accumulated DC energy is consumed by the backscattering communication, the DC voltage would reduce and reach a second level (e.g., logic low bias), the switchis switched back on and the deviceoperates in the WPH mode again. The devicecan therefore realize the switching of the operations between WPH and backscattering communications modes in a self-adaptive and periodic manner.

shows the two different ways of using RF power by the device: WPH and HB communications. When receiving RF signals from a SWIPT or similar transceiver, the received RF signals can be utilized in two possible ways. One is being converted into DC energy (i.e., WPH mode) and the other one can be upconverted into second harmonic component (i.e., HB mode). In the WPH mode, RF signals are converted at fto DC (0 Hz), fbeing the fundamental frequency of the received RF signals; and in the HB mode, the RF signals can be upconverted to 2f, as shown in. When the received RF signals pass the nonlinear element, two possibilities emerge, going through the WPH pathor backscattering path. In this exemplary embodiment, the backscattering communication is transmitted at 2f. However, those skilled in the art would appreciate that the harmonic backscattering module can triple, or quadruple the operating frequency or more, depending on the specific designs and applications of the system.

is a schematic diagram of a single-ended backscattering device, according to an exemplary embodiment of this disclosure. According to this embodiment, the backscattering devicecomprises a first portfor receiving RF signals at a fundamental frequency fand a second portfor transmitting backscattered RF signals. In accordance with this embodiment, the backscattered RF signals can be transmitted at an upconverted frequency of 2f. The devicecomprises a non-linear element(including but not limited to a diode), operably coupled to the first portand the second portThe non-linear elementallows the current to flow in one direction from the first port(input) generally to the second port(output).

According to this embodiment, the devicecan further comprise two quarter-wavelength stubs,for maximizing power conversion from fto 2f, and input and output matching networks,for maximum power transfer at fand 2f, respectively.

The non-linear elementsits in the middle of the deviceand is coupled to the first and second portsthrough the two quarter-wavelength stubs,. These two quarter-wavelength stubs,help maximize power conversion (i.e., increasing conversion efficiency) from fundamental RF fto its second harmonic component 2fin the harmonic communication mode. The quarter-wavelength stubat an input side of the non-linear elementis a short stub (i.e., short-circuited at its free end), and the quarter-wavelength stubat an output side of the non-linear elementis an open stub (i.e., left open at its free end).

The input and output matching networks,are designed for impedance matching. The input and output matching networks,can each comprise an open stub. In particular, the input matching networkis configured to allow more incident RF signals to pass which can maximize input power transfer of incident RF signals at ffor both WPH and backscattering communications modes. The output matching networkis configured to allow more generated second harmonic component to pass which can maximize power transfer of the second harmonic component 2ffor the backscattering communications mode.

The non-linear elementis also operably coupled to a WPH loadthrough a switchfor the operation change between WPH and backscattering communications modes. The switchis placed at the end of the output matching network's open stub, as shown in.

When the switchis on, the WPH loadis connected to the device, as illustrated in. The deviceoperates in the WPH mode and harvests RF power from the incident RF signals. Reference characterand the dotted line inare used to demonstrate the path of the RF signals in this mode. The RF signals generally seek a path of the lowest impedance to complete their circuit loop. The switchis normally turned on, thereby establishing a ground path for RF. As shown in, the quarter-wavelength stuband the WPH load are connected to the ground. In the WPH mode, all fundamental and higher harmonic components are grounded due to a filtering capacitanceat the WPH load. Little second harmonic signal should be generated at the second portInstead, DC energy and voltage accumulate across the load resistancethrough path. This harvested DC energy or power are then used to turn the switchoff (disconnected from the WPH load), as will be explained in more detail below.